I just happened upon this trick when testing what it was like filming from inside my guitar. *Note this effect is due to the rolling shutter, which is non-representative of how strings actually vibrate.

Tips: • You must have the strings brightly backlit to get the camera to capture at such a high frame rate (pure conjecture). You can see how the effect fades when the buildings come into view.• Use a pencil*This was used with the front facing camera, try the back camera, it may capture better! (tried it, it didn't look as good for me)